The prior art describes methods and apparatus whereby highway trailers can be assembled into a train of rail cars by removably attaching the highway trailers to rail trucks (or bogies) with wheels appropriate to rail travel; the rail trucks being detached when the trailers are to be used as normal highway units.
In the prior art of U.S. Pat. No. 5,040,466, the coupling means between the trailers when used in the rail mode is of a style which includes a forward projecting (male) coupling tongue at the front of each trailer and a complimentary (female) socket at the rear of each trailer, together with a vertical pin passing through both the tongue and the socket to effect a coupling between them. In this prior art, a standard three-piece rail truck is surmounted by an adapter pedestal unit. The adapter pedestal unit is mounted within the center of the rail truck bolster in the same way that corresponding elements of a rail car would be mounted. That is, it has a circular flat center plate at its lower surface, with the center plate riding within the central "bowl" which is part of the rail truck bolster. It thus has the ability to rotate and rock as required by the motions of the car traveling on the track. The rail truck is equipped with normal coil springs which are able to deflect as required by the superimposed load. In order to mount the railtruck/adapter combination beneath the rear of a highway trailer for use on the rails it is necessary that the rear of the trailer be raised enough for the insertion of the railtruck/adapter unit. Additionally, it is also necessary that the adapter be high enough to ensure that once the loaded trailer is placed upon it, the highway wheels of the trailer will not touch the railroad track when the rail truck springs deflect under load. The usual method for raising the trailer to mount it upon the railtruck/adapter is by the use of an air-spring highway suspension on the trailer. This trailer suspension system, such as that manufactured by Nu-Way, Granning or Fruehauf, is customarily arranged to allow for the injection of excess air into the springs; the excess air causing the rear of a trailer so equipped to be lifted above its normal highway operating height to allow the railtruck/adapter unit to be placed beneath it. This air-spring highway suspension unit also has the ability to retract its axles still further once the railtruck/adapter unit is in place, thus raising the highway wheels clear of the tracks. Other methods for raising the trailers are also used acceptably. For example, it is also practical to simply lift the rear of the trailer by external or internal mechanical or hydraulic means, or by the use of a ramp for the trailer wheels. Placing the railtruck/adapter unit in a depressed track or lowering it with a lift table will also permit the trailer to be backed over it.
In the prior art of Pat. No. 5,107,772, a special rail truck is described. This special rail truck is comprised of a rail-wheel mounted chassis and a frame mounted above this chassis. This frame has attached to it, two "fifth wheel" units such as those normally found on a conventional highway tractor used for pulling semi-trailers. Trailers used with this rail truck are fitted with vertical, downward-projecting kingpins; one at each end of the trailers. In use, the trailers are backed over the fifth wheel units so that the kingpins enter the apertures of the fifth wheels. The rail wheels of this special rail truck are air-sprung, but the rail wheels are not steerable along the railroad track. It has been mathematically proved that the kingpin/fifth-wheel combination above described does not have sufficient strength to pull safely more than (perhaps) six loaded trailers at best. This is in part because the kingpin is in a single-shear arrangement. This inadequacy of kingpin strength is made up for by the use of intermediate traction units interspersed along the train, as shown in U.S. Pat. No. 5,107,772 and further in U.S. Pat. No. 5,009,169.
Another patent which discloses a rail truck which is adapted to support one end of each of two adjacent highway trailers is GB 2,150,900. A lifting coupling is at each end of the rail truck, the lifting coupling being provided with a load bearing surface and a pivot pin, the pivot pin being received within a suitable socket at an end of the highway trailer. This construction also has the disadvantage in that only a few trailers can be pulled because the pivot pin is also in single shear arrangement.
U.S. Pat. No. 4,955,144 also describes an intermodal rail truck unit which is detachable from specially-constructed trailers. The rail truck unit is equipped with two transverse bolsters, each of which is of a width to receive and support either end of a semitrailer or ISO container; the trailers or containers being attached to the aforesaid transverse bolsters by vertically-oriented, upwardly projecting twist-lock fittings near the outer ends of the bolsters, and similar to those customarily used in the attachment of ISO containers to each other and to ships or railroad cars transporting them. These twist-lock fittings are in a single-shear arrangement with respect to the tailer supporting bolsters. As in the case of the kingpins used in U.S. Pat. No. 5,107,772 described above, this single shear arrangement can be mathematically proved to be of insufficient strength to pull a train safely. U.S. Pat. No. 4,955,144 further describes the rail trucks used with this system as having a "rigid chassis." A rail truck having a rigid chassis is incapable of providing any steering of the individual rail axles. Additionally, the patent describes a train makeup and breakup procedure wherein the trailers and/or containers are lifted by an overhead crane into position atop the rail truck bolsters, over the upwardly-projecting twist-lock fittings located near the ends of the transverse trailer support bolsters. No procedure for train makeup or breakup other than lifting the trailers is described.
In all of the above prior art, disadvantages can be identified. For example, the requirement that in some prior art designs the rear of the trailers must be lifted or that the railtruck/adapters must be lowered for attachment beneath the trailers requires equipment which adds weight to the trailer, as does the inclusion of a coupler tongue and a coupler socket as part of the trailer structure. The use of fittings such as kingpins, pivot pins, or twist-locks for pulling a train of rail cars is not a structurally sound practice. Further, it is highly desirable that modern rail trucks have a capability for limited axle steering in order that they can perform more safely on poor tracks and at higher speeds on good tracks.